The achievement of blood compatibility through the "mimicry" of the surface of platelet and red blood cell membranes is the goal of this project. A modified phospholipid fatty acid chain is covalently grafted to an aminated surface (e.g. glass, polypropylene, or PTFE), resulting in a surface containing a number of exposed polar head groups of phospholipid molecules. Earlier work showed a significant reduction in the number of adherent platelets on phosphatidylcholine-containing glass. AFM images suggested that the grafted molecule reorganizes when hydrated; cold-stage XPS is being employed at NESAC/BIO to study the surface in its hydrated state. Initial results suggest that the polar head groups are not at the outermost surface in the hydrated state.